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<script>
    // 数字  (整数 小数 ,  正值 负值 0)
    // NaN  
    // Infinity 
    // NaN  Infinity  =>  也是属于数字的范畴

    var a = 1;
    var b = 0;
    var c = a / b; // 1/0
    console.log(c,typeof c);   // Infinity 无穷大/正无穷/∞


    var a = "$10";   // 非数字"$10" 和 数字进行运算
    var b = 2;
    var c = a * b;
    console.log(c,typeof c) ; //  NaN (not a number)





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